HawaiiGST
Probationary Member
- 2
- 0
- Feb 24, 2010
-
honolulu,
Hawaii
I saw a very nice How-To on the FAQ forum for a fiberglass bumper.What i saw that the post lacked was cutting down sanding time. Which is a neccessity, yes, but one that can be shortened by a substantial amount of time. Im leaving out the prep. pretty straight forward. i also do not list exact mixtures of catalyst to resin, read the label...it should give you a table and measurements for proper mixture. when i say hotter, that means a little more catalyst than normal, which will depend on how much your mixing at one time. Experiment before hand and read a few things online about resins. Big benefit in the long run.usually the mixture listed on the label is adequate for a what i call 'slow cure'
http://www.dsmtuners.com/forums/articles-exterior-interior/99912-repairing-your-bumper-dummies.html....i felt it lacked a few key components and short cuts. Being new....i figured this was the best place to post?
I live in Hawaii, surf everyday and work on surfboards every day. Fiberglass and i have a nice relationship...an itchy one, but nice.
i can post pictures and answer questions if need be. Just ask
i have the most experience with the UV cure resin, but have a fair amount of experience with using standard catalyst curing resins as well ( you can use catalyst with UV if no sunlight is present as well)
1. you have to determine what weight/strength cloth you need anything above 8 in the surfboard industry is extreme. Most boards consist of doubling either 6 or 4 to create strength versus going up a weight, and surfboards take a BEATING when it comes to flex, tensile strength, UV damage, and overall wear and tear. using a lowest weight possible is the key to sanding less. If you need more strength consider laying layers of a lesser cloth versus going up a weight. The 4-6 weight will obviously be thinner and therefore MUCH easier to 'blend' into the existing bumper/side skirt/etc. (read "less elbow grease") proper 'coverage' and layers( applying patch many inches past the repair area) will insure more strength with a lesser weight cloth, than going to thicker heavier cloth.
2.Cut your first piece of glass 4-6 inches bigger than the crack the major fault i saw in the FAQ repair was that he didnt put any glass or repair on the visible side of the bumper. he did all his work on the unvisible side. meaning that the bumper will still be prone to cracking in the same spot. if anything the repairs should have been done on the VISIBLE side if you were going to pick just one side. better to do both. take a branch and bend it...slice the outside curve of the branch and watch it split like an over ripe peach. ever get a cut on your elbow or knee? what happens when you flex it? essentially your bumper will react the same. where would you patch the branch? where the split is on the outside. the key to making it easier on your elbows sanding wise is to start with a patch 4-6 inches bigger than the actual crack. then cut another patch 2-3 inches smaller. then one more even smaller. these layers ( more about applying them later) will essentailly raise the height of your patch and add strength. try to stick to ovals,or circles. Straight line cuts will break right on the line if it does break. get all of your patches cut and test fitted before you touch any resin.
3. Resin..... thinly resin your prepped area, i mean thinly!!! just enought to get the glass to stick, and enough so that the glass will move if pulled. To thin (picture spray glue) and once that glass hits it, it aint going no where. to thick and your glass will slide after youve got it in place. apply first patch layer. layer on some resin and use a bondo scraper/leveler/crappy paint brush( clean new brush!!) to try and saturate the cloth but use as little resin as possible...you want to be able to "see" the texture of the cloth. but have it soaked in resin. scrap excess resin away. Repeat for as many layers as needed.
*sidenote* i use UV resin so i apply my second patch after i expose it to sunlight for 3-10 seconds. its just enough sunlight to start the process and makes the resin gel enough so my first 'patch' doesnt move or i get any more resin 'underneath' my first patch.
if your using a catalyst i recommend a slower curing for the patching process. it makes for a more flexible resin and therefore patch. use fast cure on the surface 'filler coats' to get the hard , sandable finish. Faster cure makes it more brittle and hard, slower is more flexible and softer. mix up resin in as many containers as you have patches. add your catalyst ( however much you'll need) to every new container as you finish each patch. gives you enough cure time to get the last patch to 'gel' so you can apply the next and enables you to not have to waste resin when it sets up in your container but you have 3 more layers to go.
misconceptions about resin....without the glass...resin is useless for any kind of strength. the molecules are strong but very short and depend on the cloth for any kind of strength. If you use resin without glass....it WILL crack 100% of the time. FYI
3. filler coat or coatsyouve got your layers of glass down using as little resin as possible. technically your done as far as strength goes. Now this is where you are going to cut down...or lengthen... elbow grease time. Filler coats are used to bring the level of patched area closer to the surrounding area. there is a little strength drawn from it but thats not its essentail function. do thin coats. it may take 3-5 depending on how many layers of the patch you laid down. mix your resin with your catalyst on the hot side ( faster cure i.e. more catalyst) . using your brush ( buy the cheap wooden handled ones for like a 1$ a piece) brush on long strokes over all of your area and an inch or two past the biggest patch. make sure to get a nice even coat. repeat until your whole patch is 98% smooth resin. each coat should go a little further and further out of the biggest patch giving you a slow transition into yoru glass instead of a ridge.. Your glass will slowly dissapear under coats of resin. you may have the edges of your topmost patch showing just a touch, thats ok. as you brush on your resin make sure to try and use light strokes. your goal here is to smooth out the WHOLE patch. uneven resin just makes more elbow grease. using 3 layers of 6 ounce glass i usually need about 4 thin coats to successfully hide the glass and blend it into the the surrounding area. Now...at this stage is where you can smooth out transtions where you had to cut weird angles of glass to fit in nooks and crannies of your bumper, or overlap the glass only at some points ( which creates high points) trying to get around a corner in your bumper. this is also the point where you can make your life a whole lot easier in those tight spaces only your little finger can fit into to sand. Just pay extra attention to those spaces when layering glass to make everything as smooth as possible then use the resin to make it even better. it will minimize the cussing and 55 minute sanding marathons with each finger and multiple grits.
4. sanding thing about sanding is that this is where you seperate the men from the sausaged finger clutz. sanding is an art. use a block or some sort of rigid and flat tool whenever possible. using your hand (if your not careful) will create valleys and ridges because of pressure you apply with each finger or side of your hand. obviously your gonna have to wrap some paper round your hand at some point. When you do, remember to always do long consistent strokes and never do them at the same angle/spot more than a few times especially if you are applying heavy pressure with the lower grits. stop often and run your hand over your work to assess ridges and valleys. Use a machine when you can. vibrating sanders are crucial for not taking off to much material and getting that finished looked in higher grits especially for beginners. ryobi makes the sander i use. its got a pyramid shaped head for getting into nooks and crannies but a decent surface area for making sure im sanding FLAT and comes with all the grits you'll need. if you got the balls and experience you can use the disc sanders that only spin or use a disc atatchment on a drill ( which is what i use) ....beware...the are not for the inexperienced or the faint of heart. yes they make the job faster by a longshot but one twitch of the wrong muscle could put you back 10 hours. not to mention you have to be able to sand FLAT with them, even when you have to hold it at an angle to get ridges out...again, dont say i didnt warn ya. i usually take it from 60-80 grit to get most of the big stuff down and get a rough blend ( if you did your filler coats and glassing correctly this will be a quick sand with the 60-80)then to 100-150 to take down the smaller hills and valleys using light pressure. Then i switched to the vibrating sander with 200-220 and apply a fair amount of pressure. then......
5. bondo or resin? after you got a pretty smooth finish on your patch....you may find that your sanding into the glass in a few spots you dont want to or have a ridge between a funky angle you had to lay 2 pieces of glass over or have little pockets of resin that are a touch lower.after everything feels pretty good to the touch and to the eye... this is where you can either lay on another ( final) resin coat, or you can use bondo as the finisher. I would use bondo just because its a proven paintable and easily sanded material. not to mention faster to mix-apply-sand then fiberglass. hell , you can even use bondo after your patches are applied and use instead of resin for your filler. its all personal preference. if you were to use bondo as a filler i would recommend one more layer of glass just to be sure in your number of patches. the final resin or bondo, you shouldnt need to start at 80 grit. you should jump immediatly to 180-220 as your not trying to take off to much material, just blend a little. ive even jumped right to my 280 wetsanding straight from the final coat due to my prep and previous work being on the money. use your discretion. You do want to take your 'final' coat up to a paintable grit. so i start with 280 wetsand and use it sparingly or lightly, its a heavy grit. go straight to 400 wet or so after 280 and realllly work that paper . then 600-800 again really working it. Also this is a good time to evaluate your work before you get to deep into your 'final' sand...if you still got major dips, pockets, or uneveness at 220 then you have to go back to another resin/bondo coat or even maybe using some glass.
6. primer and paint whether you use bondo or not...i would always recommend an adhesion promoter. Also use a thicker 'filler' primer if your doing a bumper or something with alot of nooks and crannies. it will help hide some of the realllly hard to reach sanding areas where you just couldnt get in there good enough. ive had really weird things happen with different colors ( admittingly from a can, thats all i need in the surfboard arena) not sticking or acting very strangely on the resin. obviously you want to make sure the area is free of grease, and do your typical paint prep. but ive found that bondo makes a great paintable finish when i fixed automotive fiberglass.
7. Notes
not everything is going to cut out perfect when your cutting your patches out of glass, especially in a bumper situation. i still use layers, your first layer may look like a jigsaw puzzle trying to rap around corners...but as you lay down more you can just make sure by the top layer its nice and strong over the parts that look sketchy... focus on the crack to be repaired. make sure the last layer is what you would lay over the crack if it were 'duct tape'. sometimes you have to cut straight lines as well...just make sure its layered properly with other glass.
also...you can put as many 'final' coats on as you need...you may have to re-work an area many times to get it right...sanding and using filler coats will get you there and this is where bondo will cut down sandign time as bondo typically goes on thicker than resin..just make sure you have a good solid patch below it and your not sanding into the first layer of our patch unless its the VERY edge of the first patch of glass.
bondo is softer than resin....if your sanding them side by side, the bondo will want to stay lower than the resin....making it extrememly difficult to finish sand. go light pressure as possible and use coats of filler primer to hide the differences.. OR make sure you dont sand through top coat of bondo. OR dont use bodno. you got options.
good luck. its not rocket science but it sure is hard sometimes. Respect the process. continually i find myself sanding more than i should because i thought " i can just sand that ridge out..." when i should have filler coated better. in a perfect job you should be able to start with 150 grit after your last filler coat. the closer to perfection you can get it when you filler coat the easier your life will be.
http://www.dsmtuners.com/forums/articles-exterior-interior/99912-repairing-your-bumper-dummies.html....i felt it lacked a few key components and short cuts. Being new....i figured this was the best place to post?
I live in Hawaii, surf everyday and work on surfboards every day. Fiberglass and i have a nice relationship...an itchy one, but nice.
i can post pictures and answer questions if need be. Just ask
i have the most experience with the UV cure resin, but have a fair amount of experience with using standard catalyst curing resins as well ( you can use catalyst with UV if no sunlight is present as well)
1. you have to determine what weight/strength cloth you need anything above 8 in the surfboard industry is extreme. Most boards consist of doubling either 6 or 4 to create strength versus going up a weight, and surfboards take a BEATING when it comes to flex, tensile strength, UV damage, and overall wear and tear. using a lowest weight possible is the key to sanding less. If you need more strength consider laying layers of a lesser cloth versus going up a weight. The 4-6 weight will obviously be thinner and therefore MUCH easier to 'blend' into the existing bumper/side skirt/etc. (read "less elbow grease") proper 'coverage' and layers( applying patch many inches past the repair area) will insure more strength with a lesser weight cloth, than going to thicker heavier cloth.
2.Cut your first piece of glass 4-6 inches bigger than the crack the major fault i saw in the FAQ repair was that he didnt put any glass or repair on the visible side of the bumper. he did all his work on the unvisible side. meaning that the bumper will still be prone to cracking in the same spot. if anything the repairs should have been done on the VISIBLE side if you were going to pick just one side. better to do both. take a branch and bend it...slice the outside curve of the branch and watch it split like an over ripe peach. ever get a cut on your elbow or knee? what happens when you flex it? essentially your bumper will react the same. where would you patch the branch? where the split is on the outside. the key to making it easier on your elbows sanding wise is to start with a patch 4-6 inches bigger than the actual crack. then cut another patch 2-3 inches smaller. then one more even smaller. these layers ( more about applying them later) will essentailly raise the height of your patch and add strength. try to stick to ovals,or circles. Straight line cuts will break right on the line if it does break. get all of your patches cut and test fitted before you touch any resin.
3. Resin..... thinly resin your prepped area, i mean thinly!!! just enought to get the glass to stick, and enough so that the glass will move if pulled. To thin (picture spray glue) and once that glass hits it, it aint going no where. to thick and your glass will slide after youve got it in place. apply first patch layer. layer on some resin and use a bondo scraper/leveler/crappy paint brush( clean new brush!!) to try and saturate the cloth but use as little resin as possible...you want to be able to "see" the texture of the cloth. but have it soaked in resin. scrap excess resin away. Repeat for as many layers as needed.
*sidenote* i use UV resin so i apply my second patch after i expose it to sunlight for 3-10 seconds. its just enough sunlight to start the process and makes the resin gel enough so my first 'patch' doesnt move or i get any more resin 'underneath' my first patch.
if your using a catalyst i recommend a slower curing for the patching process. it makes for a more flexible resin and therefore patch. use fast cure on the surface 'filler coats' to get the hard , sandable finish. Faster cure makes it more brittle and hard, slower is more flexible and softer. mix up resin in as many containers as you have patches. add your catalyst ( however much you'll need) to every new container as you finish each patch. gives you enough cure time to get the last patch to 'gel' so you can apply the next and enables you to not have to waste resin when it sets up in your container but you have 3 more layers to go.
misconceptions about resin....without the glass...resin is useless for any kind of strength. the molecules are strong but very short and depend on the cloth for any kind of strength. If you use resin without glass....it WILL crack 100% of the time. FYI
3. filler coat or coatsyouve got your layers of glass down using as little resin as possible. technically your done as far as strength goes. Now this is where you are going to cut down...or lengthen... elbow grease time. Filler coats are used to bring the level of patched area closer to the surrounding area. there is a little strength drawn from it but thats not its essentail function. do thin coats. it may take 3-5 depending on how many layers of the patch you laid down. mix your resin with your catalyst on the hot side ( faster cure i.e. more catalyst) . using your brush ( buy the cheap wooden handled ones for like a 1$ a piece) brush on long strokes over all of your area and an inch or two past the biggest patch. make sure to get a nice even coat. repeat until your whole patch is 98% smooth resin. each coat should go a little further and further out of the biggest patch giving you a slow transition into yoru glass instead of a ridge.. Your glass will slowly dissapear under coats of resin. you may have the edges of your topmost patch showing just a touch, thats ok. as you brush on your resin make sure to try and use light strokes. your goal here is to smooth out the WHOLE patch. uneven resin just makes more elbow grease. using 3 layers of 6 ounce glass i usually need about 4 thin coats to successfully hide the glass and blend it into the the surrounding area. Now...at this stage is where you can smooth out transtions where you had to cut weird angles of glass to fit in nooks and crannies of your bumper, or overlap the glass only at some points ( which creates high points) trying to get around a corner in your bumper. this is also the point where you can make your life a whole lot easier in those tight spaces only your little finger can fit into to sand. Just pay extra attention to those spaces when layering glass to make everything as smooth as possible then use the resin to make it even better. it will minimize the cussing and 55 minute sanding marathons with each finger and multiple grits.
4. sanding thing about sanding is that this is where you seperate the men from the sausaged finger clutz. sanding is an art. use a block or some sort of rigid and flat tool whenever possible. using your hand (if your not careful) will create valleys and ridges because of pressure you apply with each finger or side of your hand. obviously your gonna have to wrap some paper round your hand at some point. When you do, remember to always do long consistent strokes and never do them at the same angle/spot more than a few times especially if you are applying heavy pressure with the lower grits. stop often and run your hand over your work to assess ridges and valleys. Use a machine when you can. vibrating sanders are crucial for not taking off to much material and getting that finished looked in higher grits especially for beginners. ryobi makes the sander i use. its got a pyramid shaped head for getting into nooks and crannies but a decent surface area for making sure im sanding FLAT and comes with all the grits you'll need. if you got the balls and experience you can use the disc sanders that only spin or use a disc atatchment on a drill ( which is what i use) ....beware...the are not for the inexperienced or the faint of heart. yes they make the job faster by a longshot but one twitch of the wrong muscle could put you back 10 hours. not to mention you have to be able to sand FLAT with them, even when you have to hold it at an angle to get ridges out...again, dont say i didnt warn ya. i usually take it from 60-80 grit to get most of the big stuff down and get a rough blend ( if you did your filler coats and glassing correctly this will be a quick sand with the 60-80)then to 100-150 to take down the smaller hills and valleys using light pressure. Then i switched to the vibrating sander with 200-220 and apply a fair amount of pressure. then......
5. bondo or resin? after you got a pretty smooth finish on your patch....you may find that your sanding into the glass in a few spots you dont want to or have a ridge between a funky angle you had to lay 2 pieces of glass over or have little pockets of resin that are a touch lower.after everything feels pretty good to the touch and to the eye... this is where you can either lay on another ( final) resin coat, or you can use bondo as the finisher. I would use bondo just because its a proven paintable and easily sanded material. not to mention faster to mix-apply-sand then fiberglass. hell , you can even use bondo after your patches are applied and use instead of resin for your filler. its all personal preference. if you were to use bondo as a filler i would recommend one more layer of glass just to be sure in your number of patches. the final resin or bondo, you shouldnt need to start at 80 grit. you should jump immediatly to 180-220 as your not trying to take off to much material, just blend a little. ive even jumped right to my 280 wetsanding straight from the final coat due to my prep and previous work being on the money. use your discretion. You do want to take your 'final' coat up to a paintable grit. so i start with 280 wetsand and use it sparingly or lightly, its a heavy grit. go straight to 400 wet or so after 280 and realllly work that paper . then 600-800 again really working it. Also this is a good time to evaluate your work before you get to deep into your 'final' sand...if you still got major dips, pockets, or uneveness at 220 then you have to go back to another resin/bondo coat or even maybe using some glass.
6. primer and paint whether you use bondo or not...i would always recommend an adhesion promoter. Also use a thicker 'filler' primer if your doing a bumper or something with alot of nooks and crannies. it will help hide some of the realllly hard to reach sanding areas where you just couldnt get in there good enough. ive had really weird things happen with different colors ( admittingly from a can, thats all i need in the surfboard arena) not sticking or acting very strangely on the resin. obviously you want to make sure the area is free of grease, and do your typical paint prep. but ive found that bondo makes a great paintable finish when i fixed automotive fiberglass.
7. Notes
not everything is going to cut out perfect when your cutting your patches out of glass, especially in a bumper situation. i still use layers, your first layer may look like a jigsaw puzzle trying to rap around corners...but as you lay down more you can just make sure by the top layer its nice and strong over the parts that look sketchy... focus on the crack to be repaired. make sure the last layer is what you would lay over the crack if it were 'duct tape'. sometimes you have to cut straight lines as well...just make sure its layered properly with other glass.
also...you can put as many 'final' coats on as you need...you may have to re-work an area many times to get it right...sanding and using filler coats will get you there and this is where bondo will cut down sandign time as bondo typically goes on thicker than resin..just make sure you have a good solid patch below it and your not sanding into the first layer of our patch unless its the VERY edge of the first patch of glass.
bondo is softer than resin....if your sanding them side by side, the bondo will want to stay lower than the resin....making it extrememly difficult to finish sand. go light pressure as possible and use coats of filler primer to hide the differences.. OR make sure you dont sand through top coat of bondo. OR dont use bodno. you got options.
good luck. its not rocket science but it sure is hard sometimes. Respect the process. continually i find myself sanding more than i should because i thought " i can just sand that ridge out..." when i should have filler coated better. in a perfect job you should be able to start with 150 grit after your last filler coat. the closer to perfection you can get it when you filler coat the easier your life will be.
